In the process of fabricating semiconductor devices such as LSI devices, a lamination of various kinds of thin layers including metallic layers and insulative layers are formed on a silicon wafer, for example, in order to fabricate a semiconductor substrate. During this fabrication process, a surface of each thin layer is planarized. As one major for planarizing the surface of each thin layer, chemical mechanical polishing (hereinafter referred to as “CMP”) is known. According to the CMP process, a thin disk-shaped polishing pad of synthetic resin material or expanded material thereof may be employed, and the polishing pad and the wafer (semiconductor substrate) are made to undergo relative rotation while supplying between the wafer and the pad a slurry consisting of fine particles and a suitable kind of liquid, for effect polishing.
In order to realize a highly integrated, high-precision semiconductor device, it is required to produce multiple layers of intricate patterns of extremely fine lines. To meet this end, the CMP process is required to ensure polishing precision, i.e. the ability to polish an entire wafer surface with highly precise planarization. Higher circuit densities seen in semiconductor devices in recent years have raised the bar still further as regards polishing precision in the CMP process, as well as polishing efficiency.
To realize such an advance polishing precision and planarization capacity, the polishing pad, as well known, needs somewhat elasticity depending on materials of the pad and the wafer, a required polishing precision, and the like. Namely, with the somewhat elasticity given to the polishing pad, the surface of the polishing pad is able to meet in accordance with the irregularities on the surface of the wafer, making it possible to enhance the polishing precision. However, one surface of the polishing pad, which is actually utilized for polishing (a processing surface), is required to be hard for the purpose of securing durability of the polishing pad and polishing efficiency, thereby making it difficult to give sufficient elasticity to the polishing pad. In short, for polishing pads of conventional structure, it was still exceedingly difficult to achieve both “polishing precision” and “polishing efficiency” at levels adequate to meet requirements.
In the field of super LSI in particular, metallic interconnect or metallization width of lines formed on the wafer (line patterns with metal line) is extremely narrow, i.e. 0.1 μm or smaller, and polishing is carried out at an uniformity of 2% or smaller. Also, the use of recently soft metal such as copper and gold for metallization has entered the stage of research directed to practical application. In view of the above, still further improvements are required to polishing pads in order to achieve satisfactory levels of polishing precision and polishing efficiency.
In view of the aforementioned problems, a multi-layered polishing pad has been proposed (see Patent Document No. 1). Such a multi-layered polishing pad generally has a multi-layered structure wherein a front layer made of a material rigid enough to realize physical properties required for a processing layer and a back layer made of an elastic material like a compression fiber material impregnated with resin are bonded together. That is, the back layer will exhibit elasticity and the front layer will ensure polishing efficiency, whereby both “polishing precision” and “polishing efficiency” can be achieved.
However, such a multi-layered polishing pad has the problem that it is difficult to manufacture, and the problem that there is a likelihood of interface debonding between the layers. Thus, the multi-layered polishing pad still has a room for improvement.
Patent Document No. 2 (JP-A-2001-18165), on the other hand, discloses a single-layer polishing pad made of a single material, wherein linear grooves are formed into the back surface in order to produce elasticity tending to lack. According to this polishing pad, the elasticity of the pad can be enhanced mechanically by means of the groove open in the pad back surface, so that this polishing pad is able to improve polishing precision by the given elasticity, while maintaining polishing efficiency by its front surface. Unlike the multi-layered polishing pad, this type of polishing pad is free from the problem of difficulty in manufacture and the problem of interface debonding.
However, the polishing pad as disclosed in Patent Document No. 2, has several inherent problems, and it is not enough for practical use.
Namely, the conventional polishing pad as disclosed in Patent Document No. 2 has the following problems (1)-(4):    (Problem 1) Depending on a material of the polishing pad, it is difficult to realize sufficient elasticity by just forming grooves into the back surface of the pad. In particular, if a plurality of grooves are formed into the back surface of the pad in order to exhibit desired elasticity, a surface area of the back surface where no groove is formed is made small substantially. This makes it difficult to obtain a sufficient bonding surface of the polishing pad against a rotational platen. Therefore, a possible number of grooves to be formed into the back surface of the pad may be limited.    (Problem 2) In order to compensate the elasticity of the polishing pad which tends to be insufficient only by a groove formation on the back surface, it is possible to form grooves also in the front surface of the pad. However, the groove formation on both the front and back surfaces of the polishing pad makes it very complicate to manufacture the polishing pad, leading to anxiety about the sharp decline in production efficiency.    (Problem 3) In the case of the polishing pad in which the front and back surfaces are distinguished from each other depending on molding conditions or the like, once grooves are formed on both the front and back surfaces of the pad, it becomes difficult to distinguish the front and back surfaces from each other. Therefore, the polishing pad may be placed on the platen upside down, possibly causing insufficient polishing.    (Problem 4) The groove formation on the back surface of the polishing pad causes decrease in the bonding surface area of the polishing pad against the rotational platen by an area of openings of the grooves. In addition, when a polishing process is carried out using slurry or the like, as in the CMP process, the slurry is likely to be spread over a wide area on the back surface of the polishing pad. As a result, the polishing pad is likely to be separate from the rotational platen or the like.(Patent Document No. 1)JP 11-156701A(Patent Document No. 2)JP 2001-18165 A